Neuromodulation using modulated pulse train

ABSTRACT

A neuromodulation system comprises a plurality of electrical terminals configured for being respectively coupled to a plurality of electrodes, a user interface configured for receiving input from a user that selects one of a plurality of different shapes of a modulating signal and/or selects one of a plurality of different electrical pulse parameters of an electrical pulse train, neuromodulation output circuitry configured for outputting an electrical pulse train to the plurality of electrical terminals, and pulse train modulation circuitry configured for modulating the electrical pulse train in accordance with the selected shape of the modulating signal and/or selected electrical pulse parameter of the electrical pulse train.

RELATED APPLICATION DATA

The present application is a continuation of U.S. application Ser. No.15/426,776, filed Feb. 7, 2017, which is a continuation of U.S.application Ser. No. 14/920,229, filed Oct. 22, 2015, which is acontinuation of U.S. application Ser. No. 14/195,632, filed Mar. 3,2014, now issued as U.S. Pat. No. 9,174,053, which claims the benefitunder 35 U.S.C. § 119 to U.S. provisional patent application Ser. No.61/774,835, filed Mar. 8, 2013. The foregoing applications are herebyincorporated by reference into the present application in theirentirety.

FIELD OF THE INVENTION

The present invention relates to neuromodulation systems, and moreparticularly, to neuromodulation system utilizing electrical pulsetrains.

BACKGROUND OF THE INVENTION

Implantable neuromodulation systems have proven therapeutic in a widevariety of diseases and disorders. Pacemakers and Implantable CardiacDefibrillators (ICDs) have proven highly effective in the treatment of anumber of cardiac conditions (e.g., arrhythmias). Spinal CordStimulation (SCS) systems have long been accepted as a therapeuticmodality for the treatment of chronic pain syndromes, and theapplication of tissue stimulation has begun to expand to additionalapplications such as angina pectoralis and incontinence. Deep BrainStimulation (DBS) has also been applied therapeutically for well over adecade for the treatment of refractory chronic pain syndromes, and DBShas also recently been applied in additional areas such as movementdisorders and epilepsy. Further, in recent investigations, PeripheralNerve Stimulation (PNS) systems have demonstrated efficacy in thetreatment of chronic pain syndromes and incontinence, and a number ofadditional applications are currently under investigation. Furthermore,Functional Electrical Stimulation (FES) systems, such as the Freehandsystem by NeuroControl (Cleveland, Ohio), have been applied to restoresome functionality to paralyzed extremities in spinal cord injurypatients.

These implantable neuromodulation systems typically include one or moreelectrode carrying modulation leads, which are implanted at the desiredstimulation site, and a neuromodulator (e.g., an implantable pulsegenerator (IPG)) implanted remotely from the stimulation site, butcoupled either directly to the neuromodulation lead(s) or indirectly tothe neuromodulation lead(s) via a lead extension. The neuromodulationsystem may further comprise a handheld patient programmer to remotelyinstruct the neuromodulator to generate electrical stimulation pulses inaccordance with selected stimulation parameters. The handheld programmerin the form of a remote control (RC) may, itself, be programmed by aclinician, for example, by using a clinician's programmer (CP), whichtypically includes a general purpose computer, such as a laptop, with aprogramming software package installed thereon.

Electrical modulation energy may be delivered from the neuromodulator tothe electrodes in the form of a pulsed electrical waveform. Thus,modulation energy may be controllably delivered to the electrodes tomodulate neural tissue. The combination of electrodes used to deliverelectrical pulses to the targeted tissue constitutes an electrodecombination, with the electrodes capable of being selectively programmedto act as anodes (positive), cathodes (negative), or left off (zero). Inother words, an electrode combination represents the polarity beingpositive, negative, or zero. Other parameters that may be controlled orvaried include the amplitude, duration, and rate of the electricalpulses provided through the electrode array. Each electrode combination,along with the electrical pulse parameters, can be referred to as a“neuromodulation parameter set.”

Of course, neuromodulators are active devices requiring energy foroperation, and thus, the neurostimulation system may oftentimes includesan external charger to recharge a neuromodulator, so that a surgicalprocedure to replace a power depleted neuromodulator can be avoided. Towirelessly convey energy between the external charger and the implantedneuromodulator, the charger typically includes an alternating current(AC) charging coil that supplies energy to a similar charging coillocated in or on the neurostimulation device. The energy received by thecharging coil located on the neuromodulator can then be used to directlypower the electronic componentry contained within the neuromodulator, orcan be stored in a rechargeable battery within the neuromodulator, whichcan then be used to power the electronic componentry on-demand.

In the context of an SCS procedure, one or more leads are introducedthrough the patient's back into the epidural space, such that theelectrodes carried by the leads are arranged in a desired pattern andspacing to create an electrode array. After proper placement of theleads at the target area of the spinal cord, the leads are anchored inplace at an exit site to prevent movement of the leads. To facilitatethe location of the neuromodulator away from the exit point of theleads, lead extensions are sometimes used. The leads, or the leadextensions, are then connected to the IPG, which can then be operated togenerate electrical pulses that are delivered, through the electrodes,to the targeted spinal cord tissue. The modulation, and in theconventional case, the stimulation, creates the sensation known asparesthesia, which can be characterized as an alternative sensation thatreplaces the pain signals sensed by the patient. The efficacy of SCS isrelated to the ability to modulate the spinal cord tissue correspondingto evoked paresthesia in the region of the body where the patientexperiences pain. Thus, the working clinical paradigm is thatachievement of an effective result from SCS depends on theneuromodulation lead or leads being placed in a location (bothlongitudinal and lateral) relative to the spinal tissue such that theelectrical modulation will induce paresthesia located in approximatelythe same place in the patient's body as the pain (i.e., the target oftreatment).

Conventional neuromodulation therapies employ electrical stimulationpulse trains at low- to mid-frequencies (e.g., less than 1500 Hz) toefficiently induce desired firing rate of action potentials fromelectrical pulses (e.g., one pulse can induce a burst of actionpotentials, or multiple pulses may be temporally integrated to induce onaction potential). Such stimulation pulse trains are usually tonic(i.e., the pulse amplitude, pulse rate, and pulse width are fixed).However, neuron response is a dynamic time course that can vary with thesequential stimulation, thereby limiting the volume of neural tissuethat may be consistently stimulated. Furthermore, it is known thatneural tissue may accommodate, adapt, and/or habituate to a continuoustonic input, resulting in a diminished neural response over time.

Recently, high frequency modulation (e.g., 1.5 KHz-50 KHz), which hasbeen increasingly attractive in neuromodulation for pain management, isemployed to block naturally occurring action potentials within neuralfibers or otherwise disrupt the action potentials within the neuralfibers. Although the underlying mechanisms of high frequency modulationfor pain reduction are yet unclear, it has been hypothesized that thereare many mechanisms that potentially play a role in reducing pain,including the depletion of neurotransmitter during the sustainedmodulation, desynchronized firing of multiple neurons, and generation ofstochastic noise in neuronal signal transmission or lesioning of paininformation. One disadvantage of high-frequency pulsed electrical energyis that it consumes an excessive amount of energy, thereby requiring theneuromodulator device to be charged more often.

Furthermore, although certain conventional stimulation parameters (e.g.,pulse amplitude, pulse frequency, and pulse width) of the pulsedelectrical energy, whether delivered at a low-, mid-, or high-frequency,can be varied to optimize the therapy, it may be desirable to allow theuser to vary other characteristics of the pulsed electrical energy inorder to further tailor the pulsed electrical energy to the volume ofneural tissue to be modulated.

There, thus, remains an improved technique for delivering pulsedelectrical energy to a patient.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present inventions, aneuromodulation system comprises a plurality of electrical terminalsconfigured for being respectively coupled to a plurality of electrodes,a user interface configured for receiving input from a user that definesa shape of a modulating signal, and neuromodulation output circuitryconfigured for outputting an electrical pulse train to the plurality ofelectrical terminals. The neuromodulation system further comprises pulsetrain modulation circuitry configured for modulating the electricalpulse train in accordance with the defined shape of the modulatingsignal. In one embodiment, one of a pulse amplitude, a pulse rate, and apulse duration of the electrical pulse train is modulated by theamplitude of the modulating signal. In another embodiment, the userinput comprises a selection of one of a plurality of differentpredefined shapes of the modulating signal (e.g., at least two of asinusoidal wave, a triangular wave, and a ramp wave). In still anotherembodiment, the user interface is configured for receiving another inputfrom the user selecting an electrical pulse parameter of the electricalpulse train to be modulated, and the pulse train modulation circuitry isconfigured for modulating the selected electrical pulse parameter of theelectrical pulse train in accordance with the defined shape of themodulating signal. The neuromodulation system may further comprise acasing containing the plurality of electrical terminals, the userinterface, the neuromodulation output circuitry, and the electricalpulse modulation circuitry.

In accordance with a second aspect of the present inventions, aneuromodulation system comprises a plurality of electrical terminalsconfigured for being respectively coupled to a plurality of electrodes,a user interface configured for receiving an input from a user selectingone of a plurality of different electrical pulse parameters for anelectrical pulse train (e.g., at least two of a sinusoidal wave, atriangular wave, and a ramp wave), and neuromodulation output circuitryconfigured for outputting the electrical pulse train to the plurality ofelectrical terminals. The neuromodulation system further comprises pulsetrain modulation circuitry configured for modulating the selectedelectrical pulse parameter of the electrical pulse train. Theneuromodulation system may further comprise a casing containing theplurality of electrical terminals, the user interface, theneuromodulation output circuitry, and the electrical pulse modulationcircuitry.

In accordance with a third aspect of the present inventions, aneuromodulation system comprises a plurality of electrical terminalsconfigured for being respectively coupled to a plurality of electrodes,neuromodulation output circuitry configured for outputting an electricalpulse train to the plurality of electrical terminals, and pulse trainmodulation circuitry configured for modulating a pulse rate of theelectrical pulse train in accordance with a determinate modulatingsignal. The neuromodulation system may optionally comprise a userinterface configured for receiving an input from a user defining acharacteristic of the modulating signal. In one embodiment, thecharacteristic of the modulating signal is a shape of the modulatingsignal. In this case, the user input may comprise a selection of one ofa plurality of different predefined shapes of the modulating signal(e.g., at least two of a sinusoidal wave, a triangular wave, and a rampwave. The neuromodulation system may further comprise a casingcontaining the plurality of electrical terminals, the neuromodulationoutput circuitry, and the electrical pulse modulation circuitry.

In accordance with a fourth aspect of the present inventions, aneuromodulation system comprises a plurality of electrical terminalsconfigured for being respectively coupled to a plurality of electrodes,neuromodulation output circuitry configured for outputting an electricalpulse train to the plurality of electrical terminals, and pulse trainmodulation circuitry configured for modulating a pulse duration of theelectrical pulse train in accordance with a determinate modulatingsignal. The neuromodulation system may optionally comprise a userinterface configured for receiving an input from a user defining acharacteristic of the modulating signal. In one embodiment, thecharacteristic of the modulating signal is a shape of the modulatingsignal. In this case, the user input may comprise a selection of one ofa plurality of different predefined shapes of the modulating signal(e.g., at least two of a sinusoidal wave, a triangular wave, and a rampwave. The neuromodulation system may further comprise a casingcontaining the plurality of electrical terminals, the neuromodulationoutput circuitry, and the electrical pulse modulation circuitry.

Other and further aspects and features of the invention will be evidentfrom reading the following detailed description of the preferredembodiments, which are intended to illustrate, not limit, the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate the design and utility of preferred embodimentsof the present invention, in which similar elements are referred to bycommon reference numerals. In order to better appreciate how theabove-recited and other advantages and objects of the present inventionsare obtained, a more particular description of the present inventionsbriefly described above will be rendered by reference to specificembodiments thereof, which are illustrated in the accompanying drawings.Understanding that these drawings depict only typical embodiments of theinvention and are not therefore to be considered limiting of its scope,the invention will be described and explained with additionalspecificity and detail through the use of the accompanying drawings inwhich:

FIG. 1 is a plan view of an embodiment of a spinal cord modulation (SCM)system arranged in accordance with the present inventions;

FIG. 2 is a plan view of the SCM system of FIG. 1 in use with a patient;

FIG. 3 is a profile view of an implantable pulse generator (IPG) andpercutaneous leads used in the SCM system of FIG. 1;

FIG. 4 is a plot of monophasic cathodic electrical modulation energy;

FIG. 5a is a plot of biphasic electrical modulation energy having acathodic modulation pulse and an active charge recovery pulse;

FIG. 5b is a plot of biphasic electrical modulation energy having acathodic modulation pulse and a passive charge recovery pulse;

FIG. 6a is a diagram illustrating a pulse amplitude of an electricalpulse train modulated with a sinusoidal wave in accordance with onemodulation technique performed by the SCM system of FIG. 1;

FIG. 6b is a diagram illustrating a pulse amplitude of an electricalpulse train modulated with a triangular wave in accordance with onemodulation technique performed by the SCM system of FIG. 1;

FIG. 6c is a diagram illustrating a pulse amplitude of an electricalpulse train modulated with a ramped wave in accordance with onemodulation technique performed by the SCM system of FIG. 1;

FIG. 6d is a diagram illustrating a pulse amplitude of an electricalpulse train modulated with a stepped sinusoidal wave in accordance withone modulation technique performed by the SCM system of FIG. 1;

FIG. 7a is a diagram illustrating a pulse rate of an electrical pulsetrain modulated with a sinusoidal wave in accordance with one modulationtechnique performed by the SCM system of FIG. 1;

FIG. 7b is a diagram illustrating a pulse rate of an electrical pulsetrain modulated with a triangular wave in accordance with one modulationtechnique performed by the SCM system of FIG. 1;

FIG. 7c is a diagram illustrating a pulse rate of an electrical pulsetrain modulated with a ramped wave in accordance with one modulationtechnique performed by the SCM system of FIG. 1;

FIG. 8a is a diagram illustrating a pulse duration of an electricalpulse train modulated with a sinusoidal wave in accordance with onemodulation technique performed by the SCM system of FIG. 1;

FIG. 8b is a diagram illustrating a pulse duration of an electricalpulse train modulated with a triangular wave in accordance with onemodulation technique performed by the SCM system of FIG. 1;

FIG. 8c is a diagram illustrating a pulse duration of an electricalpulse train modulated with a ramped wave in accordance with onemodulation technique performed by the SCM system of FIG. 1;

FIG. 9 is a block diagram of the internal components of the IPG of FIG.3;

FIG. 10 is front view of a remote control (RC) used in theneuromodulation system of FIG. 1;

FIG. 11 is a block diagram of the internal components of the RC of FIG.10;

FIG. 12 is a plan view of a programming screen generated by the RC ofFIG. 10 for modulating an electrical pulse train.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The description that follows relates to a spinal cord modulation (SCM)system. However, it is to be understood that while the invention lendsitself well to applications in spinal cord modulation, the invention, inits broadest aspects, may not be so limited. Rather, the invention maybe used with any type of implantable electrical circuitry used tostimulate tissue. For example, the present invention may be used as partof a pacemaker, a defibrillator, a cochlear stimulator, a retinalstimulator, a stimulator configured to produce coordinated limbmovement, a cortical stimulator, a deep brain stimulator, peripheralnerve stimulator, microstimulator, or in any other neurostimulatorconfigured to treat urinary incontinence, sleep apnea, shouldersublaxation, headache, etc.

Turning first to FIG. 1, an exemplary SCM neuromodulation system 10generally includes one or more (in this case, two) implantablemodulation leads 12, an implantable pulse generator (IPG) 14, anexternal remote controller RC 16, a clinician's programmer (CP) 18, anExternal Trial Modulator (ETM) 20, and an external charger 22.

The IPG 14 is physically connected via one or more percutaneous leadextensions 24 to the neuromodulation leads 12, which carry a pluralityof electrodes 26 arranged in an array. In the illustrated embodiment,the neuromodulation leads 12 are percutaneous leads, and to this end,the electrodes 26 may be arranged in-line along the neuromodulationleads 12. In alternative embodiments, the electrodes 26 may be arrangedin a two-dimensional pattern on a single paddle lead. As will bedescribed in further detail below, the IPG 14 includes pulse generationcircuitry that delivers electrical modulation energy in the form of apulsed electrical waveform (i.e., a temporal series of electricalpulses) to the electrode array 26 in accordance with a set ofneuromodulation parameters.

The ETM 20 may also be physically connected via the percutaneous leadextensions 28 and external cable 30 to the neuromodulation leads 12. TheETM 20, which has similar pulse generation circuitry as the IPG 14, alsodelivers electrical modulation energy in the form of a pulse electricalwaveform to the electrode array 26 accordance with a set ofneuromodulation parameters. The major difference between the ETM 20 andthe IPG 14 is that the ETM 20 is a non-implantable device that is usedon a trial basis after the neuromodulation leads 12 have been implantedand prior to implantation of the IPG 14, to test the responsiveness ofthe stimulation that is to be provided. Thus, any functions describedherein with respect to the IPG 14 can likewise be performed with respectto the ETM 20.

The RC 16 may be used to telemetrically control the ETM 20 via abi-directional RF communications link 32. Once the IPG 14 and modulationleads 12 are implanted, the RC 16 may be used to telemetrically controlthe IPG 14 via a bi-directional RF communications link 34. Such controlallows the IPG 14 to be turned on or off and to be programmed withdifferent neuromodulation parameter sets. The IPG 14 may also beoperated to modify the programmed neuromodulation parameters to activelycontrol the characteristics of the electrical modulation energy outputby the IPG 14. As will be described in further detail below, the CP 18provides clinician detailed neuromodulation parameters for programmingthe IPG 14 and ETM 20 in the operating room and in follow-up sessions.

The CP 18 may perform this function by indirectly communicating with theIPG 14 or ETM 20, through the RC 16, via an IR communications link 36.Alternatively, the CP 18 may directly communicate with the IPG 14 or ETM20 via an RF communications link (not shown). The clinician detailedneuromodulation parameters provided by the CP 18 are also used toprogram the RC 16, so that the neuromodulation parameters can besubsequently modified by operation of the RC 16 in a stand-alone mode(i.e., without the assistance of the CP 18).

The external charger 22 is a portable device used to transcutaneouslycharge the IPG 14 via an inductive link 38. For purposes of brevity, thedetails of the external charger 22 will not be described herein. Oncethe IPG 14 has been programmed, and its power source has been charged bythe external charger 22 or otherwise replenished, the IPG 14 mayfunction as programmed without the RC 16 or CP 18 being present.

For purposes of brevity, the details of the ETM 20 and external charger22 will not be described herein. Details of exemplary embodiments ofthese devices are disclosed in U.S. Pat. No. 6,895,280, which isexpressly incorporated herein by reference.

As shown in FIG. 2, the neuromodulation leads (or lead) 12 are implantedwithin the spinal column 42 of a patient 40. The preferred placement ofthe neuromodulation leads 12 is adjacent, i.e., resting near, or uponthe dura, adjacent to the spinal cord area to be stimulated. Theneuromodulation leads 12 will be located in a vertebral position thatdepends upon the location and distribution of the chronic pain. Forexample, if the chronic pain is in the lower back or legs, theneuromodulation leads 12 may be located in the mid- to low-thoracicregion (e.g., at the T9-12 vertebral levels). Due to the lack of spacenear the location where the neuromodulation leads 12 exit the spinalcolumn 42, the IPG 14 is generally implanted in a surgically-made pocketeither in the abdomen or above the buttocks. The IPG 14 may, of course,also be implanted in other locations of the patient's body. The leadextensions 24 facilitate locating the IPG 14 away from the exit point ofthe electrode leads 12. As there shown, the CP 18 communicates with theIPG 14 via the RC 16.

Referring now to FIG. 3, the features of the neuromodulation leads 12and the IPG 14 will be briefly described. One of the neuromodulationleads 12(1) has eight electrodes 26 (labeled E1-E8), and the othermodulation lead 12(2) has eight electrodes 26 (labeled E9-E16). Theactual number and shape of leads and electrodes will, of course, varyaccording to the intended application. The IPG 14 comprises an outercase 44 for housing the electronic and other components (described infurther detail below), and a connector 46 to which the proximal ends ofthe neuromodulation leads 12 mates in a manner that electrically couplesthe electrodes 26 to the electronics within the outer case 40. The outercase 44 is composed of an electrically conductive, biocompatiblematerial, such as titanium, and forms a hermetically sealed compartmentwherein the internal electronics are protected from the body tissue andfluids. In some cases, the outer case 40 may serve as an electrode.

As will be described in further detail below, the IPG 14 includes abattery and pulse generation circuitry that delivers the electricalmodulation energy in the form of one or more electrical pulse trains tothe electrode array 26 in accordance with a set of neuromodulationparameters programmed into the IPG 14. Such neuromodulation parametersmay comprise electrode combinations, which define the electrodes thatare activated as anodes (positive), cathodes (negative), and turned off(zero), percentage of modulation energy assigned to each electrode(fractionalized electrode configurations), and electrical pulseparameters, which define the pulse amplitude (measured in milliamps orvolts depending on whether the IPG 14 supplies constant current orconstant voltage to the electrode array 26), pulse duration (measured inmicroseconds), pulse rate (measured in pulses per second), and burstrate (measured as the modulation on duration X and modulation offduration Y).

Electrical modulation will occur between two (or more) activatedelectrodes, one of which may be the IPG case 44. Modulation energy maybe transmitted to the tissue in a monopolar or multipolar (e.g.,bipolar, tripolar, etc.) fashion. Monopolar modulation occurs when aselected one of the lead electrodes 26 is activated along with the caseof the IPG 14, so that modulation energy is transmitted between theselected electrode 26 and case. Bipolar modulation occurs when two ofthe lead electrodes 26 are activated as anode and cathode, so thatmodulation energy is transmitted between the selected electrodes 26. Forexample, electrode E3 on the first lead 12(1) may be activated as ananode at the same time that electrode E11 on the second lead 12(1) isactivated as a cathode. Tripolar modulation occurs when three of thelead electrodes 26 are activated, two as anodes and the remaining one asa cathode, or two as cathodes and the remaining one as an anode. Forexample, electrodes E4 and E5 on the first lead 12 may be activated asanodes at the same time that electrode E12 on the second lead 12 isactivated as a cathode

The modulation energy may be delivered between a specified group ofelectrodes as monophasic electrical energy or multiphasic electricalenergy. As illustrated in FIG. 4, monophasic electrical energy takes theform of an electrical pulse train that includes either all negativepulses (cathodic), or alternatively all positive pulses (anodic).

Multiphasic electrical energy includes a series of pulses that alternatebetween positive and negative. For example, as illustrated in FIGS. 5aand 5b , multiphasic electrical energy may include a series of biphasicpulses, with each biphasic pulse including a cathodic (negative)modulation pulse (during a first phase) and an anodic (positive) chargerecovery pulse (during a second phase) that is generated after themodulation pulse to prevent direct current charge transfer through thetissue, thereby avoiding electrode degradation and cell trauma. That is,charge is conveyed through the electrode-tissue interface via current atan electrode during a modulation period (the length of the modulationpulse), and then pulled back off the electrode-tissue interface via anoppositely polarized current at the same electrode during a rechargeperiod (the length of the charge recovery pulse).

The second phase may have an active charge recovery pulse (FIG. 5a ),wherein electrical current is actively conveyed through the electrodevia current or voltage sources, and a passive charge recovery pulse, orthe second phase may have a passive charge recovery pulse (FIG. 5b ),wherein electrical current is passively conveyed through the electrodevia redistribution of the charge flowing from coupling capacitancespresent in the circuit. Using active recharge, as opposed to passiverecharge, allows faster recharge, while avoiding the charge imbalancethat could otherwise occur. Another electrical pulse parameter in theform of an interphase can define the time period between the pulses ofthe biphasic pulse (measured in microseconds).

Significant to the present inventions, the SCM system 10 is capable ofallowing a user to define an electrical pulse parameter (e.g., a pulseamplitude, pulse rate, and/or a pulse duration) of an electrical pulsetrain that is to be modulated with a determinate modulation signal. TheSCM system may also be capable of allowing a user to define the shape(e.g., sinusoidal, triangular, ramp, etc) of the modulation signal thatis to be used to modulate the electrical pulse train. In this manner,more flexibility is provided to the user to tailor the pulsed electricalenergy to the targeted volume of neural tissue to be modulated.Furthermore, for low- or mid-frequency applications (i.e., less than1500 Hz), accommodation of the neural tissue may be prevented orotherwise minimized without having to expend a considerable amount ofenergy that might otherwise occur by utilizing high-frequency electricalenergy. It is also proposed that the modulation of a low- ormid-frequency pulse train may desynchronize the firing of actionpotentials in the neural tissue at a reduced energy consumption.

The amplitude of a relatively high frequency electrical pulse train maybe modulated by a relatively low frequency modulating signal to createan electrical pulse train having an envelope that varies in accordancewith the amplitude of the modulating signal (i.e., as the amplitude ofthe modulating signal increases, the envelope of electrical pulse trainincreases, and as the amplitude of the modulating signal decreases, theenvelope of the electrical pulse train decreases). For example, asillustrated in FIG. 6a , the amplitude of an electrical pulse train canbe modulated by a sinusoidal modulating signal to create an electricalpulse train with a sinusoid shaped envelope. As illustrated in FIG. 6b ,the amplitude of an electrical pulse train can be modulated by atriangular modulating signal to create an electrical pulse train with atriangle shaped envelope. As illustrated in FIG. 6c , the amplitude ofan electrical pulse train can be modulated by a ramped modulating signalto create an electrical pulse train with a ramp shaped envelope.Although the ramped modulating signal is shown as being linearlyincreasing, the ramped modulating signal may alternatively be linearlydecreasing, or even non-linearly increasing or decreasing (e.g.,exponential). The electrical pulse train can be alternately turned onand off to create a modulated bursted electrical pulse train. Forexample, as illustrated in FIG. 6d , the amplitude of an electricalpulse train can be modulated by the combination of a sinusoidalmodulating signal and a stepped signal to create a bursted electricalpulse train with a sinusoid shaped envelope.

The pulse rate of a relatively high frequency electrical pulse train maybe modulated by a relatively low frequency modulating signal to createan electrical pulse train having a pulse rate that varies in accordancewith the amplitude of the modulating signal (i.e., as the amplitude ofthe modulating signal increases, the pulse rate increases, and as theamplitude of the modulating signal decreases, the pulse rate decreases).For example, as illustrated in FIG. 7a , the pulse rate of an electricalpulse train can be modulated by a sinusoidal modulating signal to createan electrical pulse train having a pulse rate that varies in accordancewith the amplitude of the sinusoidal modulating signal. As illustratedin FIG. 7b , the pulse rate of an electrical pulse train can bemodulated by a triangular modulating signal to create an electricalpulse train having a pulse rate that varies in accordance with theamplitude of the triangular modulating signal. As illustrated in FIG. 7c, the pulse rate of an electrical pulse train can be modulated by aramped modulating signal to create an electrical pulse train having apulse rate that varies in accordance with the amplitude of the rampedmodulating signal. Although a single timing channel is utilized tocreate the modulated electrical pulse trains illustrated in FIGS. 7a-7c, electrical pulse trains with different pulse rates can be bursted onand off in multiple timing channels to create a single electrical pulsetrain with a modulated pulse rate, as described in U.S. ProvisionalPatent Application Ser. No. 61/768,286, entitled “Multi-ChannelNeuromodulation System Having Frequency Modulated Stimulation,” which isexpressly incorporated herein by reference.

The pulse duration of a relatively high frequency electrical pulse trainmay be modulated by a relatively low frequency modulating signal tocreate an electrical pulse train having a pulse duration that varies inaccordance with the amplitude of the modulating signal (i.e., as theamplitude of the modulating signal increases, the pulse durationincreases, and as the amplitude of the modulating signal decreases, thepulse duration decreases). For example, as illustrated in FIG. 8a , thepulse duration of an electrical pulse train can be modulated by asinusoidal modulating signal to create an electrical pulse train havinga pulse duration that varies in accordance with the amplitude of thesinusoidal modulating signal. As illustrated in FIG. 8b , the pulseduration of an electrical pulse train can be modulated by a triangularmodulating signal to create an electrical pulse train having a pulseduration that varies in accordance with the amplitude of the triangularmodulating signal. As illustrated in FIG. 8c , the pulse duration of anelectrical pulse train can be modulated by a ramped modulating signal tocreate an electrical pulse train having a pulse duration that varies inaccordance with the amplitude of the ramped modulating signal.

Although the modulations of the electrical pulse trains illustratedabove are biphasic in nature, it should be appreciated that themodulation of an electrical pulse train can be monophasic in nature; forexample, by modulating the amplitudes of only the cathodic phases of theelectrical pulse train.

Turning next to FIG. 9, the main internal components of the IPG 14 willnow be described. The IPG 14 includes neuromodulation output circuitry50 configured for generating electrical modulation energy in accordancewith a defined pulsed waveform having a specified pulse amplitude, pulserate, pulse width, pulse shape, and burst rate under control of controllogic 52 over data bus 54. Control of the pulse rate and pulse width ofthe electrical waveform is facilitated by timer logic circuitry 56,which may have a suitable resolution, e.g., 10 μs. The neuromodulationenergy generated by the neuromodulation output circuitry 50 is outputvia capacitors C1-C16 to electrical terminals 58 corresponding to theelectrodes 26. The neuromodulation circuitry 50 may either compriseindependently controlled current sources for providing modulation pulsesof a specified and known amperage to or from the electrodes 26, orindependently controlled voltage sources for providing modulation pulsesof a specified and known voltage at the electrodes 26.

Any of the N electrodes may be assigned to up to k possible groups ortiming “channels.” In one embodiment, k may equal four. The timingchannel identifies which electrodes are selected to synchronously sourceor sink current to create an electric field in the tissue to bestimulated. Amplitudes and polarities of electrodes on a channel mayvary, e.g., as controlled by the RC 16. External programming software inthe CP 18 is typically used to set neuromodulation parameters includingelectrode polarity, amplitude, pulse rate and pulse duration for theelectrodes of a given channel, among other possible programmablefeatures.

The N programmable electrodes can be programmed to have a positive(sourcing current), negative (sinking current), or off (no current)polarity in any of the k channels. Moreover, each of the N electrodescan operate in a multipolar (e.g., bipolar) mode, e.g., where two ormore electrode contacts are grouped to source/sink current at the sametime. Alternatively, each of the N electrodes can operate in a monopolarmode where, e.g., the electrode contacts associated with a channel areconfigured as cathodes (negative), and the case electrode (i.e., the IPGcase) is configured as an anode (positive).

Further, the amplitude of the current pulse being sourced or sunk to orfrom a given electrode may be programmed to one of several discretecurrent levels, e.g., between 0 to 10 mA in steps of 0.1 mA. Also, thepulse duration of the current pulses is preferably adjustable inconvenient increments, e.g., from 0 to 1 milliseconds (ms) in incrementsof 10 microseconds (μs). Similarly, the pulse rate is preferablyadjustable within acceptable limits, e.g., from 0 to 50000 pulses persecond (pps). Other programmable features can include slow start/endramping, burst modulation cycling (on for X time, off for Y time),interphase, and open or closed loop sensing modes.

The operation of this neuromodulation output circuitry 50, includingalternative embodiments of suitable output circuitry for performing thesame function of generating modulation pulses of a prescribed amplitudeand duration, is described more fully in U.S. Pat. Nos. 6,516,227 and6,993,384, which are expressly incorporated herein by reference.

The IPG 14 further comprises pulse train modulation circuitry 60configured for using predeterminate modulation signals (e.g., themodulating signals illustrated in FIGS. 6-8 to modulate electrical pulsetrain output by the neuromodulation output circuitry 50 to theelectrical terminals 58. In response to user input, as will be describedin further detail below, the modulation circuitry 60 may advantageouslyselect the particular electrical parameter (e.g., pulse amplitude, pulserate, and/or pulse duration) of the electrical pulse train and/or selectthe shape of the modulation signal (e.g., sinusoidal, triangular,ramped, etc.) used to modulate the electrical pulse train. Themodulation circuitry 60 may be analog-based and incorporated into theoutput of the neuromodulation output circuitry 50 and/or may bedigitally-based and incorporated into the control logic 52 and timerlogic circuitry 56.

The IPG 14 further comprises monitoring circuitry 62 for monitoring thestatus of various nodes or other points 64 throughout the IPG 14, e.g.,power supply voltages, temperature, battery voltage, and the like. TheIPG 14 further comprises processing circuitry in the form of amicrocontroller (μC) 66 that controls the control logic over data bus68, and obtains status data from the monitoring circuitry 62 via databus 70. The IPG 14 additionally controls the timer logic 56. The IPG 14further comprises memory 72 and oscillator and clock circuitry 74coupled to the microcontroller 66. The microcontroller 66, incombination with the memory 72 and oscillator and clock circuitry 74,thus comprise a microprocessor system that carries out a programfunction in accordance with a suitable program stored in the memory 72.Alternatively, for some applications, the function provided by themicroprocessor system may be carried out by a suitable state machine.

Thus, the microcontroller 66 generates the necessary control and statussignals, which allow the microcontroller 66 to control the operation ofthe IPG 14 in accordance with a selected operating program andneuromodulation parameters stored in the memory 72. In controlling theoperation of the IPG 14, the microcontroller 66 is able to individuallygenerate an electrical pulse train at the electrodes 26 using theneuromodulation output circuitry 50, in combination with the controllogic 52 and timer logic 56, thereby allowing each electrode 26 to bepaired or grouped with other electrodes 26, including the monopolar caseelectrode. In accordance with neuromodulation parameters stored withinthe memory 72, the microcontroller 66 may control the polarity,amplitude, rate, pulse duration and timing channel through which themodulation pulses are provided.

Thus, it can be appreciated that, under control of the microcontroller66, the neuromodulation output circuitry 50 is configured for outputtinga k number of individual electrical pulse trains respectively in a knumber of timing channels to the electrical terminals 58. In the IPG 14,up to four stimulation programs may be stored in the memory 72, witheach stimulation program having four timing channels. Thus, eachmodulation program defines four sets of neuromodulation parameters forfour respective timing channels. Of course, the IPG 14 may have less ormore than four modulation programs, and less or more than four timingchannels for each modulation program. Significantly, the microcontroller66 controls the modulation circuitry 60 in a manner that, for eachtiming channel, modulates the electrical pulse train in accordance withthe electrical pulse parameter and/or shape of the modulating signalselected by the user.

The IPG 14 further comprises an alternating current (AC) receiving coil76 for receiving programming data (e.g., the operating program,neuromodulation parameters, electrical parameters to be modulated,and/or the shape of the modulating signal) from the RC 16 (shown in FIG.2) in an appropriate modulated carrier signal, and charging and forwardtelemetry circuitry 78 for demodulating the carrier signal it receivesthrough the AC receiving coil 76 to recover the programming data, whichprogramming data is then stored within the memory 72, or within othermemory elements (not shown) distributed throughout the IPG 14.

The IPG 14 further comprises back telemetry circuitry 60 and analternating current (AC) transmission coil 82 for sending informationaldata sensed through the monitoring circuitry 62 to the RC 16. The backtelemetry features of the IPG 14 also allow its status to be checked.For example, when the RC 16 initiates a programming session with the IPG14, the capacity of the battery is telemetered, so that the externalprogrammer can calculate the estimated time to recharge. Any changesmade to the current stimulus parameters are confirmed through backtelemetry, thereby assuring that such changes have been correctlyreceived and implemented within the implant system. Moreover, uponinterrogation by the RC 16, all programmable settings stored within theIPG 14 may be uploaded to the RC 16. Significantly, the back telemetryfeatures allow raw or processed electrical parameter data (or otherparameter data) previously stored in the memory 72 to be downloaded fromthe IPG 14 to the RC 16, which information can be used to track thephysical activity of the patient.

The IPG 14 further comprises a rechargeable power source 84 and powercircuits 86 for providing the operating power to the IPG 14. Therechargeable power source 84 may, e.g., comprise a lithium-ion orlithium-ion polymer battery. The rechargeable battery 84 provides anunregulated voltage to the power circuits 86. The power circuits 86, inturn, generate the various voltages 88, some of which are regulated andsome of which are not, as needed by the various circuits located withinthe IPG 14. The rechargeable power source 84 is recharged usingrectified AC power (or DC power converted from AC power through othermeans, e.g., efficient AC-to-DC converter circuits, also known as“inverter circuits”) received by the AC receiving coil 76. To rechargethe power source 84, an external charger (not shown), which generatesthe AC magnetic field, is placed against, or otherwise adjacent, to thepatient's skin over the implanted IPG 14. The AC magnetic field emittedby the external charger induces AC currents in the AC receiving coil 76.The charging and forward telemetry circuitry 78 rectifies the AC currentto produce DC current, which is used to charge the power source 84.While the AC receiving coil 76 is described as being used for bothwirelessly receiving communications (e.g., programming and control data)and charging energy from the external device, it should be appreciatedthat the AC receiving coil 76 can be arranged as a dedicated chargingcoil, while another coil, such as coil 82, can be used forbi-directional telemetry.

It should be noted that the diagram of FIG. 9 is functional only, and isnot intended to be limiting. Those of skill in the art, given thedescriptions presented herein, should be able to readily fashionnumerous types of IPG circuits, or equivalent circuits, that carry outthe functions indicated and described, which functions include not onlyproducing a stimulus current or voltage on selected groups ofelectrodes, but also the ability to measure electrical parameter data atan activated or non-activated electrode.

Additional details concerning the above-described and other IPGs may befound in U.S. Pat. No. 6,516,227, U.S. Patent Publication No.2003/0139781, and U.S. patent application Ser. No. 11/138,632, entitled“Low Power Loss Current Digital-to-Analog Converter Used in anImplantable Pulse Generator,” which are expressly incorporated herein byreference. It should be noted that rather than an IPG, the SCM system 10may alternatively utilize an implantable receiver-stimulator (not shown)connected to the neuromodulation leads 12. In this case, the powersource, e.g., a battery, for powering the implanted receiver, as well ascontrol circuitry to command the receiver-stimulator, will be containedin an external controller inductively coupled to the receiver-stimulatorvia an electromagnetic link. Data/power signals are transcutaneouslycoupled from a cable-connected transmission coil placed over theimplanted receiver-stimulator. The implanted receiver-stimulatorreceives the signal and generates the modulation in accordance with thecontrol signals.

Referring now to FIG. 10, one exemplary embodiment of an RC 16 isdescribed. As previously discussed, the RC 16 is capable ofcommunicating with the IPG 14, CP 18, or ETS 20. The RC 16 comprises acasing 100, which houses internal componentry (including a printedcircuit board (PCB)), and a lighted display screen 102 and button pad104 carried by the exterior of the casing 100. In the illustratedembodiment, the display screen 102 is a lighted flat panel displayscreen, and the button pad 104 includes a membrane switch with metaldomes positioned over a flex circuit, and a keypad connector connecteddirectly to a PCB. In an optional embodiment, the display screen 102 hastouchscreen capabilities. The button pad 104 includes a multitude ofbuttons 106, 108, 110, and 112, which allow the IPG 14 to be turned ONand OFF, provide for the adjustment or setting of neuromodulationparameters within the IPG 14, and provide for selection between screens.The button pad 104 also allows the user to select the electrical pulseparameters to be modulated and/or the shape of the modulating signalused to modulate the electrical pulse train, as will be described infurther detail below.

In the illustrated embodiment, the button 106 serves as an ON/OFF buttonthat can be actuated to turn the IPG 14 ON and OFF. The button 108serves as a select button that allows the RC 106 to switch betweenscreen displays and/or parameters. The buttons 110 and 112 serve asup/down buttons that can be actuated to increase or decrease any ofstimulation parameters of the pulse generated by the IPG 14, includingthe pulse amplitude, pulse width, and pulse rate. For example, theselection button 108 can be actuated to place the RC 16 in a “PulseAmplitude Adjustment Mode,” during which the pulse amplitude can beadjusted via the up/down buttons 110, 112, a “Pulse Width AdjustmentMode,” during which the pulse width can be adjusted via the up/downbuttons 110, 112, and a “Pulse Rate Adjustment Mode,” during which thepulse rate can be adjusted via the up/down buttons 110, 112.Alternatively, dedicated up/down buttons can be provided for eachstimulation parameter. Rather than using up/down buttons, any other typeof actuator, such as a dial, slider bar, keypad, or touch screen can beused to increment or decrement the stimulation parameters.

The selection button 108 can also be actuated to place the RC 16 in an“pulse train modulation mode” that allows a user modulate the electricalpulse train output by the IPG 14 in one of the timing channels and toselect the electrical pulse parameter to be modulated and/or the shapeof the modulating signal. For example, referring to FIG. 12, aprogramming screen 150 includes a modulation shape box 152 that includesa sinusoidal wave 154 a, a triangular wave 154 b, and a ramped wave 154c, and corresponding check boxes, any of which can be selected by theuser using the button pad 104 to select the shape of the modulatingsignal used to modulate the electrical pulse train. Optionally, theprogramming screen 150 has a modulating parameter control (not shown)that allows the user to specify modulation parameters (e.g., upper andlower limit of the modulation shape, period of modulating signal, suchas the sinusoidal wave, slope of a ramped wave, etc. The programmingscreen 150 also includes a modulated electrical pulse parameter box 156that includes a pulse amplitude check box 158 a, a pulse rate check box158 b, and a pulse duration check box 158 c, any combination of whichcan be checked using the button pad 104 to allow the user to select theelectrical pulse parameters of the electrical pulse train to bemodulated. The programming screen 150 also includes an ON/OFF check box160 that can be checked to turn the modulation feature on and uncheckedto turn the modulation feature off. When the feature is turned on, theIPG 14 will modulate the selected electrical pulse parameter orparameters of the electrical pulse train using the modulating signalwith the selected shape. The buttons 110 and 112 serve as up/downbuttons that can be actuated to increase or decrease the amplitude ofthe modulating signal.

Although the foregoing programming functions have been described asbeing at least partially implemented in the RC 16, it should be notedthat these techniques may be at least, in part, be alternatively oradditionally implemented in the CP 18. Those skilled in the art will beable to fashion appropriate circuitry, whether embodied in digitalcircuits, analog circuits, software and/or firmware, or combinationsthereof, in order to accomplish the desired functions.

Although particular embodiments of the present inventions have beenshown and described, it will be understood that it is not intended tolimit the present inventions to the preferred embodiments, and it willbe obvious to those skilled in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe present inventions. Thus, the present inventions are intended tocover alternatives, modifications, and equivalents, which may beincluded within the spirit and scope of the present inventions asdefined by the claims.

What is claimed is:
 1. A system including an external device, wherein the external device includes a user interface with a display, and wherein the external device is configured for: presenting, on the display of the external device, a plurality of waveforms available for selection by a user, wherein at least one of the plurality of waveforms comprises a modulated pulse train, wherein an attribute of at least a portion of the modulated pulse train is modulated by a modulating signal, thereby providing an attribute for each pulse of the at least the portion of the modulated pulse train that corresponds to an attribute of the modulating signal; receiving a user input through the user interface, the user input being indicative of a user selection of at least one of the plurality of waveforms presented on the display of the external device; and generating a program for a neurostimulator to deliver neuromodulation to neural tissue in accordance with the selected at least one waveform, wherein the neuromodulation delivered to neural tissue includes the modulated pulse train delivered to the neural tissue.
 2. The system of claim 1, wherein: the attribute for each pulse of the at least the portion of the modulated pulse train comprises an amplitude of the at least the portion of the modulated pulse train; and the attribute of the modulating signal comprises an amplitude of the modulating signal.
 3. The system of claim 2, wherein the modulating signal includes at least one shape selected from a plurality of shapes.
 4. The system of claim 3, wherein the modulating signal includes at least one of a sinusoidal modulation signal, a triangular modulation signal, a ramped modulation signal, or a stepped sinusoidal modulation signal.
 5. The system of claim 1, wherein: the attribute for each pulse of the at least the portion of the modulated pulse train comprises a frequency of the at least the portion of the modulated pulse train; and the attribute of the modulating signal comprises an amplitude of the modulating signal.
 6. The system of claim 5, wherein the modulating signal includes at least one of a sinusoidal modulation signal, a triangular modulation signal, a ramped modulation signal, or a stepped sinusoidal modulation signal.
 7. The system of claim 1, wherein: the attribute for each pulse of the at least the portion of the modulated pulse train comprises a pulse duration of the at least the portion of the modulated pulse train; and the attribute of the modulating signal comprises an amplitude of the modulating signal.
 8. The system of claim 1, wherein the plurality of waveforms available for selection by the user include at least one of an amplitude modulated waveform, a frequency modulated waveform, or a pulse-width modulated waveform.
 9. A system including an external device, wherein the external device includes a user interface with a display, and wherein the external device is configured for: presenting, on the display of the external device, a plurality of waveforms available for selection by a user, wherein at least one of the plurality of waveforms comprises a modulated pulse train, wherein a pulse duration attribute of at least a portion of the modulated pulse train is modulated by a modulating signal, thereby providing a pulse duration attribute for each pulse of the at least the portion of the modulated pulse train that corresponds to an attribute of the modulating signal; receiving a user input through the user interface, the user input being indicative of a user selection of at least one of the plurality of waveforms presented on the display of the external device; and generating a program for a neurostimulator to deliver neuromodulation to neural tissue in accordance with the selected at least one waveform, wherein the neuromodulation delivered to neural tissue includes the modulated pulse train delivered to the neural tissue.
 10. The system of claim 9, wherein the pulse duration attribute comprises a duration of time between a beginning of a pulse of the modulated pulse train and an end of the same pulse of the modulated pulse train, and the attribute of the modulating signal comprises an amplitude of the modulating signal.
 11. The system of claim 10, wherein the modulating signal includes at least one of a sinusoidal modulation signal, a triangular modulation signal, a ramped modulation signal, or a stepped sinusoidal modulation signal.
 12. The system of claim 11, wherein the attribute of the modulating signal comprises an amplitude of the modulating signal.
 13. The system of claim 9, wherein the pulse duration attribute comprises a duration of time between an end of a pulse of the modulated pulse train and a beginning of a subsequent pulse of the modulated pulse train, and the attribute of the modulating signal comprises an amplitude of the modulating signal.
 14. The system of claim 13, wherein the modulating signal includes at least one of a sinusoidal modulation signal, a triangular modulation signal, a ramped modulation signal, or a stepped sinusoidal modulation signal.
 15. The system of claim 14, wherein the attribute of the modulating signal comprises an amplitude of the modulating signal.
 16. The system of claim 9, wherein the plurality of waveforms available for selection by the user include at least one of an amplitude modulated waveform, a frequency modulated waveform, or a pulse-width modulated waveform.
 17. A system including an external device, wherein the external device includes a user interface with a display, and wherein the external device is configured for: presenting, on the display of the external device, a plurality of waveforms available for selection by a user, wherein at least one the plurality of waveforms comprises a modulated pulse train, wherein a pulsing frequency at which pulses pulse in the at least a portion of the modulated pulse train is modulated by a modulating signal, thereby providing a pulsing frequency for each set of pulses of the at least the portion of the modulated pulse train that corresponds to an attribute of the modulating signal; receiving a user input through the user interface, the user input being indicative of a user selection of at least one of the plurality of waveforms presented on the display of the external device; and generating a program for a neurostimulator to deliver neuromodulation to neural tissue in accordance with the selected at least one waveform, wherein the neuromodulation delivered to neural tissue includes the modulated pulse train delivered to the neural tissue.
 18. The system of claim 17, wherein the modulating signal includes at least one of a sinusoidal modulation signal, a triangular modulation signal, a ramped modulation signal, or a stepped sinusoidal modulation signal.
 19. The system of claim 18, wherein the plurality of waveforms available for selection by the user include at least one of an amplitude modulated waveform, a frequency modulated waveform, or a pulse-width modulated waveform.
 20. The system of claim 19, wherein the attribute of the modulating signal comprises an amplitude of the modulating signal. 